Pre-travel and overtravel are two commonly specified requirements for a switch. Pre-travel is the amount of movement of the switch actuator mechanism before the switch changes its electrical state, i.e., the electrical state between the switch's terminals changes. The electrical state between a pair of switch terminals is typically either an electrical open circuit or a short circuit. Overtravel is the amount of movement that the switch actuator is designed to accommodate after the switch changes state. The sum of pre-travel and overtravel is the total travel of the switch actuator.
The rise of terrorism in the world has created the need to secure and protect activities of a general commercial nature. One such need is that of securing shipping containers against unauthorized opening after the container has been readied and sealed for shipment. Electronic systems that utilize electrical switches are being designed to track and monitor containers with respect to unauthorized opening as the containers are in transit to their respective destinations. In the co-pending application, Ser. No. 11/451,193, filed Jun. 12, 2006, and assigned to the present assignee, a switch is disclosed that is intended to be mounted on the door of the shipping container to detect unauthorized opening of the container. In this application, a device limit switch is needed to accompany an electrical “black box” that would be disposed in shipping container and would communicate the location of the container to a predetermined monitoring location. The device limit switch would be mounted in each shipping container along with the electronic “black box” and would quickly respond to any attempt to tamper with or move the black box. As there is a large embedded base of shipping containers, a device limit switch for this application must be compatible with existing container designs, must be robust enough to withstand the rough treatment typically experienced by shipping containers, and must operate flawlessly. As the device limit switch must also operate with different containers and black boxes having rather large part tolerances, the switch must provide low pre-travel and high overtravel in a low height switch. While electrical switches exist in a myriad of shapes, sizes, and designs, no existing switch exists that can meet the requirements of this described shipping container application. Accordingly, providing a device limit switch for a system designed to detect unauthorized tampering or movement of the contents of a shipping container would be desirable.